title: Spider-fed bromeliads: seasonal and interspecific variation in plant performance.
abstract: OBJECTIVE
  Several animals that live on bromeliads can contribute to plant nutrition through nitrogen provisioning (digestive mutualism). The bromeliad-living spider Psecas chapoda (Salticidae) inhabits and breeds on Bromelia balansae in regions of South America, but in specific regions can also appear on Ananas comosus (pineapple) plantations and Aechmea distichantha.
  
  
  METHODS
  Using isotopic and physiological methods in greenhouse experiments, the role of labelled ((15)N) spider faeces and Drosophila melanogaster flies in the nutrition and growth of each host plant was evaluated, as well as seasonal variation in the importance of this digestive mutualism.
  
  
  RESULTS
  Spiders contributed 0·6 ± 0·2 % (mean ± s.e.; dry season) to 2·7 ± 1 % (wet season) to the total nitrogen in B. balansae, 2·4 ± 0·4 % (dry) to 4·1 ± 0·3 % (wet) in An. comosus and 3·8 ± 0·4 % (dry) to 5 ± 1 % (wet) in Ae. distichantha. In contrast, flies did not contribute to the nutrition of these bromeliads. Chlorophylls and carotenoid concentrations did not differ among treatments. Plants that received faeces had higher soluble protein concentrations and leaf growth (RGR) only during the wet season.
  
  
  CONCLUSIONS
  These results indicate that the mutualism between spiders and bromeliads is seasonally restricted, generating a conditional outcome. There was interspecific variation in nutrient uptake, probably related to each species' performance and photosynthetic pathways. Whereas B. balansae seems to use nitrogen for growth, Ae. distichantha apparently stores nitrogen for stressful nutritional conditions. Bromeliads absorbed more nitrogen coming from spider faeces than from flies, reinforcing the beneficial role played by predators in these digestive mutualisms.
authors.affiliation: Pós-graduação em Ecologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas-SP, Brazil.
authors.forename: Ana Zangirólame
authors.initials: AZ
authors.lastname: Gonçalves
authors.forename: Helenice
authors.initials: H
authors.lastname: Mercier
authors.forename: Paulo
authors.initials: P
authors.lastname: Mazzafera
authors.forename: Gustavo Quevedo
authors.initials: GQ
authors.lastname: Romero
mesh_terms: D000818:Animals; D031231:Bromelia / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D004331:Drosophila melanogaster; D005243:Feces / Q000737:chemistry; D009584:Nitrogen / Q000378:metabolism; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism; D012621:Seasons; D013045:Species Specificity; D013112:Spiders / Q000502:physiology*
chemical_list: D010940:Plant Proteins; D002734:Chlorophyll; D002338:Carotenoids; D009584:Nitrogen